As a conventional bearing device for a driving wheel, for example, there is proposed a bearing device for a driving wheel capable of facilitating assembly work with a small-sized and lightweight structure, preventing generation of harsh gear-rattling noise for a long period of time, and suppressing generation of a backlash in an axial direction without strictly regulating shape dimension accuracy (see Patent Document 1).
As illustrated in FIG. 19, the bearing device for a driving wheel disclosed in Patent Document 1 includes, as main components, a hub wheel 101, an inner race 102, double-row rolling elements 103, 104, an outer race 105, and a constant velocity universal joint 106.
The hub wheel 101 has an inner raceway surface 107 on an outboard side formed on its outer peripheral surface, and includes a wheel attachment flange 109 for being attached to a wheel (not shown). Hub bolts 110 for fixing a wheel disk are embedded at equal intervals in a circumferential direction of the wheel attachment flange 109. The inner race 102 is fit onto a small-diameter step portion 112 formed on the outer peripheral surface on an inboard side of the hub wheel 101, and an inner raceway surface 108 on the inboard side is formed on the outer peripheral surface of the inner race 102. Note that, a female spline 128 for coupling the constant velocity universal joint 106 and the hub wheel so as to be capable of transmitting torque therebetween is formed on the inner peripheral surface of a shaft hole the hub wheel 101.
The inner race 102 is press-fit with adequate interference for the purpose of, preventing creep. The inner raceway surface 107 on the outboard side formed on the outer peripheral surface of the hub wheel 101 and the inner raceway surface 108 on the inboard side formed on the outer peripheral surface of the inner race 102 constitute double-row raceway surfaces. The inner race 102 is press-fit onto the small-diameter step portion 112 of the hub wheel 101, and the end portion of the small-diameter step portion 112 of the hub wheel 101 is caulked outwardly. Consequently, the inner race 102 is prevented from slipping off by a caulked portion 111 thus obtained, and is integrated with the hub wheel 101 to apply preload to a bearing section 120.
The outer race 105 has double-row outer raceway surfaces 113, 114 formed on its inner peripheral surface and opposed to the inner raceway surfaces 107, 108 of the hub wheel 101 and the inner race 102, and includes a vehicle body attachment flange 117 for being attached to a vehicle body (not shown). The vehicle body attachment flange 117 is fitted to a knuckle extending from a suspension device (not shown) of a vehicle body, and is fixed by a bolt or the like.
The bearing section 120 has a double-row angular ball bearing structure, and has a structure in which the rolling elements 103, 104 are interposed between the inner raceway surfaces 107, 108 formed on the outer peripheral surfaces of the hub wheel 101 and the inner race 102 and the outer raceway surfaces 113, 114 formed on the inner peripheral surface of the outer race 105, and the rolling elements 103, 104 in respective rows are supported at equal intervals in the circumferential direction by a cage (not shown). Note that, a predetermined bearing gap is set inside the bearing section 120.
A pair of seals 123, 129 for sealing an annular space between the outer race 105 and the hub wheel 101 and an annular space between the outer race 105 and the inner race 102 so as to be held in slide-contact with the outer peripheral surfaces of the hub wheel 101 and the inner race 102 is fitted to the inner surface at both end portions of the outer race 105 at the openings on both ends of the bearing section 120. Further, the seals 123, 124 prevent leakage of grease filled inside and intrusion of water and foreign matters from an outside.
The constant velocity universal joint 106 is provided at one end of an intermediate shaft (not shown) constituting a drive shaft, and includes an outer joint member 115 having a track groove formed in its inner peripheral surface, an inner joint member 131 having a track groove which is formed in its outer peripheral surface and opposed to the track groove of the outer joint member 115, balls 132 incorporated between the track groove of the outer joint member 115 and the track groove of the inner joint member 131, and a cage 133 interposed between the inner peripheral surface of the outer joint member 115 and the outer peripheral surface of the inner joint member 131 for holding the balls 132. The outer joint member 115 includes a mouth section 125 accommodating the inner joint member 131, the balls 132, and the cage 133, and a stem section 127 extending integrally from the mouth section 125 in the axial direction and having a male spline 126 formed on its outer peripheral surface.
The stem section 127 of the outer joint member 115 is press-fit into the shaft hole of the hub wheel 101, and the male spline 126 formed on the outer peripheral surface of the stem section 127 and the female spline 128 formed to the shaft hole of the hub wheel 101 are fit to each other, whereby the outer joint member 115 and the hub wheel 101 are coupled to each other so as to be capable of transmitting torque therebetween. Further, the bolt 130 is screwed into the end portion of the stem section 127 of the outer joint member 115 through the intermediation of the cap 129 attached to the end portion of the hub wheel 101, whereby the constant velocity universal joint 106 is fixed to the hub wheel 101.
In the bearing device for a driving wheel disclosed in Patent Document 1, the male spline 126 formed on the outer peripheral surface of the stem section 127 of the outer joint member 115 and the female spline 128 formed on the inner peripheral surface of the shaft hole of the hub wheel 101 are tapered splines. That is, teeth of the male spline 126 are formed to have a circumferential width widening inward in the axial direction, and teeth of the female spline 128 are formed to have a circumferential width widening outward in the axial direction. Further, when the stem section 127 of the outer joint member 115 is press-fit into the shaft hole of the hub wheel 101, the male spline 126 of the stem section 127 and the female spline 128 of the hub wheel 101 are engaged with each other in a wedged manner, whereby both the members are coupled to each other so as to be capable of transmitting torque therebetween.    Patent Document 1: JP 2002-120506 A